Extend and document compiler debugging utilities (#19841)

* Add two debugutils procs that native debuggers can break on use to
  execute commands when code of interest is being compiled.
* Add GDB and LLDB programs to disable and enable breakpoints and
  watchpoints when code of interest is being compiled.
* Extend the `intern.rst` docs regarding debugging the compiler.

Co-authored-by: quantimnot <quantimnot@users.noreply.github.com>

doc/koch.rst

@@ -38,6 +38,9 @@ options:
   unless you are debugging the compiler.
 -d:nimUseLinenoise     Use the linenoise library for interactive mode
                        (not needed on Windows).
+-d:leanCompiler        Produce a compiler without JS codegen or
+                       documentation generator in order to use less RAM
+                       for bootstrapping.
 
 After compilation is finished you will hopefully end up with the nim
 compiler in the `bin` directory. You can add Nim's `bin` directory to